It is known in the art to hot pressing green mixtures of Si3N4, AlN, Al2O3 and Nd2O3, at a temperature in the range of 1550° to 1750° C., and at a pressure of about 20 MPa (Wang et al. in Mater. Res. Soc. Symp. Proc., Vol. 287, 1993, pp. 387–392 titled “Formation and densification of R-α′ SiAlONs (R=Nd,Sm,Gd, Dy,Er,Yb)”). Shen et al. (J. Am. Ceram. Soc., Vol. 79, No. 3, 1996, pp. 721–32 titled “Homogeneity region and thermal stability of neodymium—doped α SiAlON ceramics”) teach hot pressing to fabricate the material as stated above.
O'Reilly et al. (Mater. Res. Soc. Symp. Proc., Vol. 287, 1993, pp. 393–398 titled “Parameters affecting pressureless sintering of α′ SiAlONs with lanthanide modifying cations”) discloses that green mixture containing similar starting materials as above were pressureless sintered but yielded only 50% α-SiAlON in the sintered product. Kall et al. (J. Eur. Ceram. Soc., Vol. 6, 1990, pp. 191–27, titled “Sialon ceramics made with mixtures of Y2O3— Nd2O3 as sintering aids”) discloses that green mixtures were pressureless sintered above 1825° C. Although the high temperature firing could produce fully sintered material, the pressureless sintering at 1750° C. could only produce up to 96% of theoretical density even when α-SiAlON is completely absent.
The major drawbacks of the above noted hitherto known processes are that these involve selection of a composition that requires hot pressing for full densification, which is evidently expensive. It is also difficult to manufacture a complex-shaped material and also failed to produce high densification under pressure less sintering method.
Thus, there is a need to provide a composition for preparation of dense neodymium stabilised β-Si3N4-α-SiAlON composite, which overcome the above disadvantages.